1. Field of the Invention
The subject invention relates to fuel metering systems, and more particularly, to a fixed displacement vane pump for use in aircraft engines that is adapted and configured to be selectively adjusted to accommodate a range of different engine applications.
2. Background of the Related Art
For many years, main engine fuel pumps for aircraft had been configured as fixed displacement gear pumps. Fixed displacement vane pumps were developed in order to overcome certain deficiencies of gear pumps. An example of a fixed displacement vane pump is disclosed in U.S. Pat. No. 4,354,809, the disclosure of which is herein incorporated by reference in its entirety.
Vane pumps include a rotor element that has radial slots for supporting radially movable vane elements defining circumferential vane buckets. The rotor element is mounted within a cam member defining an interior cam surface. The outer tips of the vane elements are in continuous contact with the interior cam surface of the cam member. The cam surface has a fluid inlet port through which fluid is delivered to the low pressure inlet areas of the rotor surface. The fluid is subsequently compressed within the vane buckets and discharged from the high pressure outlet areas of the rotor surface as pressurized fluid.
Variable displacement vane pumps are also well known in the art, as disclosed for example in commonly assigned U.S. Pat. Nos. 5,545,014 and 5,545,018, the disclosures of which are herein incorporated by reference in their entireties. Variable displacement vane pumps have a swing cam element which pivots relative to the rotor element, so as to change the relative volumes of the inlet and outlet discharge areas, and thereby vary the displacement capacity of the pump.
In the aerospace industry, there is a broad range of engine applications that employ fixed displacement vane pumps and variable displacement vane pumps. For each application, the pumping requirements vary, thus requiring different sized pumps. Resizing new pumps for each engine application is costly, particularly in the case of variable displacement vane pumps. It would be beneficial therefore, to provide a fixed displacement vane pump that can be selectively adjusted to accommodate a wide range of different engine applications.
The subject invention is directed to a low cost fixed displacement vane pump that can be selectively adjusted to accommodate a wide range of different engine applications. The fixed displacement pump of the subject invention includes a pump housing defining an interior pumping chamber having a central axis extending therethrough. A rotor member is mounted for rotational movement within the interior pumping chamber of the pump housing about an axis aligned with the central axis of the interior pumping chamber. The rotor member has a central vane section with a plurality of circumferentially spaced apart radial vane slots formed therein. Each vane slot supports a corresponding vane element mounted for radial movement therein, and each vane element has an outer tip surface.
A cam member is mounted for pivotal movement within the interior pumping chamber of the pump housing about a fulcrum axis extending parallel to the central axis of the rotor member. The cam member defines a cam body having a circular bore extending therethrough for receiving the rotor member. The circular bore forms a cam chamber defining a cam surface making continuous contact with the outer tip surfaces of the vane elements during the rotation of the rotor member.
In addition, means are provided for selectively maintaining the cam member in a fixed position relative to the axis of the rotor member. In one embodiment of the subject invention, the means for selectively maintaining the cam member in a fixed position is preferably in the form of a pair of diametrically opposed locking bolts mounted to bear against an outer circumferential surface of the cam member. In another embodiment of the subject invention, the means for selectively maintaining the cam member in a fixed position is preferably in the form of two or more dowels mounted to engage corresponding ports formed in the outer circumferential surface of the cam member.
The means for selectively maintaining the cam member in a fixed position relative to the axis of the rotor member is adapted and configured to fix the position of the cam member in a position which ranges between a maximum eccentric position relative to the axis of the rotor member and a minimum eccentric position (or nearly concentric position) relative to the axis of the rotor. The maximum eccentric position corresponds to a maximum displacement flow condition for the pump and the minimum eccentric position corresponds to a minimum displacement flow condition for the pump.
These and other unique features of the selectively adjustable fixed displacement vane pump of the subject invention will become more readily apparent from the following description of the drawings taken in conjunction with the description of the preferred embodiment.